1. Field of the Invention
The present invention generally relates to a method of cleaning a semiconductor device. More particularly, the invention relates to a method of cleaning a semiconductor device, improved to remove Pt (Ptxe2x80x94Ir) and BST contaminants on a surface edge, a back, and a bevel of a semiconductor wafer. The invention relates to an apparatus for cleaning a semiconductor device, which realizes such a cleaning method. The invention also relates to a method of fabricating a semiconductor device, employing the cleaning method.
2. Description of the Background Art
In order to reduce the size of a semiconductor device (particularly, a dynamic random access memory (DRAM)), as dielectric materials of a capacitor, a Baxe2x80x94Srxe2x80x94Ti oxide (hereinbelow, described as BST) has started to be used. As a material of a capacitor electrode, Pt or Ptxe2x80x94Ir has started to be used. In the case of using new materials, it is important to suppress expansion of contamination by the metal elements (Ba, Sr, Ti, Pt, and Ir) on the production line. The following can be considered as one of flows in which the contamination expansion occurs.
(1) At the time of formation of a Pt (or Ptxe2x80x94Ir) film and a BST film, the films are formed not only on the surface of the semiconductor wafer but also on the back and the bevel edge of the wafer.
(2) The wafer on which the Pt (Ptxe2x80x94Ir) film and the BST film are formed is housed in a housing and carrying cassette and carried to an apparatus for performing the subsequent process. At this time, the surface edge, back, and bevel of the wafer come into contact with and rub against the cassette (cassette groove) and the groove portion of the cassette is contaminated by Ba, Sr, Ti, Pt, and Ir.
(3) When the wafer on which the Pt (Ptxe2x80x94Ir) film and the BST film are formed is carried to an apparatus of the subsequent process, a carrier system comes into contact with the surface edge, back surface edge, and bevel of the wafer. At this time, the carrier system is contaminated by Ba, Sr, Ti, Pt, and Ir.
(4) A semiconductor wafer whose surface edge, back, and bevel are not contaminated by Ba, Sr, Ti, Pt, and Ir is housed in the housing and carrying cassette used in (2). At this time, the surface edge, back, and bevel of the wafer come into contact with and rub against the cassette, and the Ba, Sr, Ti, Pt, and Ir contamination is transferred from the contaminated groove portion of the cassette to the not-contaminated semiconductor wafer.
(5) A semiconductor wafer whose surface edge, back, and bevel are not contaminated by Ba, Sr, Ti, Pt, and Ir is processed by the apparatus in (3). At this time, the surface edge, back, and bevel of the wafer come into contact with the carrier system, and the Ba, Sr, Ti, Pt, and Ir contamination is transferred from the carrier system to the wafer.
(6) By the wafer to which the contamination is transferred in (4) and (5), the contamination is expanded in (1) to (3) in the flow.
In order to prevent expansion of contamination via the carrier system (manufacturing process apparatus and housing and carrying cassette), after forming a Pt (Ptxe2x80x94Ir) film and a BST film in the semiconductor fabricating process, it is necessary to remove the BST film and the Pt (or Ptxe2x80x94Ir) film adhered on the surface edge, back, and bevel of the wafer, or remove contaminants of Ba, Sr, Ti, Pt, and Ir.
As a contamination removing method, after forming the Pt (Ptxe2x80x94Ir) film and the BST film, a chemical capable of etching the films is applied on only the surface edge, back, and bevel of a wafer to remove the films by etching.
It is also possible to perform a cleaning process after a process of forming a single film of BST-Pt (Ptxe2x80x94Ir) to remove the contaminants. However, in a normal capacitor forming flow, immediately after forming a dielectric film, an upper electrode film is formed. If the time of this period becomes long, an organic material existing in the atmosphere in a clean room is adhered to the wafer, and there is the possibility that increase in resistance is caused and the electric characteristics of the capacitor deteriorate. Consequently, the BST film and the Pt (Ptxe2x80x94Ir) film are successively formed and, subsequently, a Pt (Ptxe2x80x94Ir)-BST stacked film is formed.
According to another method of applying an etchant to the surface edge, back, and bevel of a wafer, a resist is applied on the whole surface of the wafer. After that, in order to remove the resist at the surface edge from which the contaminant is desired to be removed by dissolving, the surface edge of the wafer is rinsed. The surface of the wafer except for the edge is protected with a resist and, after that, the whole wafer is soaked in a cleaning fluid. The wafer is cleaned with water and dried and, after that, the resist is removed. In such a manner, the contaminants on the surface edge, back, and bevel edge are removed. In the method, however, in addition to the cleaning process, the resist protecting and removing process has to be performed. At the time of removing the resist, there is the possibility that a damage (including etching) and contamination of an organic material are given to the upper electrode and the wafer surface, and the electric characteristics deteriorate.
An object of the invention is, therefore, to provide a method of removing contaminants of Ba, Sr, Ti, Pt, and Ir existing on the surface edge, back, and bevel of a wafer by a single cleaning process even in the case where a (granular) Pt(Ptxe2x80x94Ir) deposit exists at the surface edge of the wafer after forming a Pt(Ptxe2x80x94Ir)-BST stacked film.
Another object of the invention is to provide a method of cleaning a semiconductor device, capable of applying a cleaning chemical only to a surface edge, back, and bevel of a wafer and removing contaminants by a single process without damaging an upper electrode and the wafer surface.
Further another object of the invention is to provide an apparatus for cleaning a semiconductor device, capable of realizing the cleaning method.
Further another object of the invention is to provide a method of fabricating a semiconductor device, including the method of cleaning a semiconductor device.
In a method of cleaning a semiconductor device according to a first aspect of the invention, first, a wafer having a surface on which a stacked film selected from the group of a Pt film, a Ptxe2x80x94Ir film, and a Baxe2x80x94Srxe2x80x94Ti film is formed is prepared (step 1). Only the surface edge, back, and bevel of the wafer are selectively cleaned (step 2).
According to a preferable embodiment of the invention, in the second step, first, a chemical containing hydrochloric acid is applied only to the surface edge, back, and bevel of the wafer. Only the surface edge, back, and bevel of the wafer are rinsed with pure water. A chemical containing hydrogen fluoride is applied only to the surface edge, back, and bevel of the wafer, and only the surface edge, back, and bevel of the wafer are rinsed again with pure water. After that the wafer is dried.
According to a further preferable embodiment of the invention, as the chemical containing hydrochloric acid, a solution of hydrochloric acid and hydrogen peroxide is used.
According to further another embodiment of the invention, as the chemical containing hydrochloric acid, a solution of hydrochloric acid and nitric acid is used.
As the solution of hydrochloric acid and nitric acid, a solution having the mixing ratio of hydrochloric acid of 30 wt % and nitric acid of 70 wt %=3:1 is used.
According to a preferable embodiment of the invention, as a chemical containing hydrogen fluoride, an organic solvent in which ammonium fluoride is dissolved is used.
According to a further preferable embodiment of the invention, in the step of applying the chemical containing hydrochloric acid only to the surface edge, back, and bevel of the wafer, first, the wafer is rotated. N2, dry air, or pure water is discharged toward the surface of the wafer. The chemical is discharged toward the back of the wafer.
In a method of fabricating a semiconductor device according to a second aspect of the invention, first, a stacked film selected from the group of a Pt film, a Ptxe2x80x94Ir film, and a Baxe2x80x94Srxe2x80x94Ti film is formed on the surface of a wafer. Only the surface edge, back, and bevel of the wafer are selectively cleaned.
An apparatus for cleaning a semiconductor device according to a third aspect of the invention includes: means for rotating a wafer; wafer surface-side discharging means for discharging N2, dry air, or pure water toward the surface of the wafer to thereby protect the surface of the wafer; and wafer back-side discharging means for discharging said chemical or pure water toward the back of said wafer.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.